This invention relates to a sprocket drum assembly for a scraper-chain conveyor of a mineral mining installation.
The scraper bars of a scraper-chain conveyor are driven along the line of conveyor pans by means of an endless chain which passes around a pair of sprocket drum assemblies positioned in a drive frame at each end of the line. At least one of the sprocket drum assemblies is keyed to a drive shaft of a drive station, though one of them may be keyed to an idler shaft. Where the scraper bars are driven by a single centre chain, the sprocket drum assembly is constituted by a generally cylindrical, hollow drum and a sprocket wheel fixed centrally to the outer cylindrical surface thereof. Where a double centre chain is used to drive the scraper bars, there are two sprocket wheels centrally positioned on the drum. Similarly, where the scraper bars are driven by a pair of outboard chains, the drum is provided with a pair of sprocket wheels positioned one adjacent each end thereof. In all cases, the sprocket wheel or wheels may be integrally formed with their drums. Although, from now on, the specification relates to a sprocket drum assembly having a single, central sprocket wheel, it will be appreciated that the invention is equally applicable to the other two types of assembly. In order to facilitate the assembly and removal of such a sprocket drum assembly, it is known to have a two-part assembly. Such an assembly has complementary parts which can be fitted to, and removed from, the associated drive (or idler) shaft without removing the shaft from the drive frame. The two parts of such an assembly are usually bolted together, and can be removed by unfastening the bolts and then withdrawing the two assembly parts radially.
In order to maintain the strength of the teeth of the sprocket wheel, the plane of separation between the two parts of the assembly is arranged to pass between two pairs of adjacent teeth. Where the sprocket wheel has an even number of teeth, there are no problems, as the plane of separation can be a diametrical plane which passes between adjacent pairs of teeth at each end. This results in an assembly in which the two parts are identical halves. Where there are an odd number of teeth, however, there are problems, since such a diametrical plane of separation will pass through a tooth at one end thereof. In order to prevent this, a known sprocket drum assembly having an odd number of teeth (see DE-OS 2340318) has a double plane of separation. Each plane of separation passes between a respective adjacent pair of teeth and the two planes meet at the axis of rotation of the assembly. This means that one part of the assembly subtends an obtuse angle at the axis and the other part subtends a reflex angle, the sum of the two angles being 360.degree.. Unfortunately, the larger part has a part-cylindrical inner surfaces which is larger than that of half a cylinder. Thus, in order to allow this part to be fitted to, and removed from, its shaft in a radial direction, it is necessary to cut away the inner longitudinal edges of this part along the entire length thereof. Not only does this involve considerable effort, but it also greatly reduces the area of contact between the inner cylindrical surface of that part and the shaft. Consequently, the surface pressure between that drum assembly part and the shaft is increased. This is particularly disadvantageous, as the areas of reduced contact occur at just the places where contact is most needed to counter the forces which tend to tilt the sprocket wheel (and hence the entire assembly) relative to the shaft. These disadvantages adversely affect such an assembly as regard its ability to transmit large torques or to take up radially or obliquely directed forces. Moreover, as these cut-away zones extend the entire length of the larger assembly part they interfere with the function of the seals provided at the two ends of the assembly for sealing the rotatable assembly with respect to the stationary drive frame parts in which the assembly is mounted.
The aim of the invention is to provide a two-part chain drum assembly having an odd number of sprocket teeth which does not require the inner longitudinal edges of the larger part to be cut away, at least in the regions not carrying sprocket teeth.